The chemical modification of surfaces to achieve desired chemical and/or physical characteristics has been previously described. Often, the various coatings and techniques referred to above are used to coat the surfaces of materials (e.g., medical devices) intended for temporary or permanent placement in the body. In turn, the resulting coatings typically provide a desired function or feature, such as lubricity, and must do so in a manner that provides the desired combination of such other properties as hemocompatability, durability, and sterility.
A number of patents generally relate to surface modification by the use of latent reactive groups to achieve covalent coupling of agents such as biomolecules and synthetic polymers to various substrates. See, for example, Applicant's U.S. Pat. Nos. 4,722,906, 4,826,759, 4,973,493, 4,979,959, 5,002,582, 5,073,484, 5,217,492, 5,258,041, 5,263,992, 5,414,075, 5,512,329, 5,512,474, 5,563,056, 5,637,460, 5,714,360, 5,741,551, 5,744,515, 5,783,502, 5,858,653, 5,942,555, 6,007,833, 6,020,147, 6,077,698, 6,090,995, 6,121,027, 6,156,345, 6,214,901 and published PCT Application Nos. US82/06148, US87/01018, US87/02675, US88/04487, US88/04491, US89/02914, US90/05028, US90/06554, US93/01248, US93/10523, US94/12659, US96/07695, US96/08797, US96/17645, US97/05344, US98/16605, US98/20140, US99/03862, US99/05244, US99/05245, US99/08310, US99/12533, US99/21247, US00/00535, US00/01944, US00/33643, and US01/40255, (each of which is commonly owned by the assignee of the invention described herein, and the disclosure of each is incorporated herein by reference). The preferred latent reactive group is often described as a photochemically reactive functional group (“photoreactive group”). When exposed to an appropriate energy source, a latent reactive (e.g., photoreactive) group undergoes a transformation from an inactive state (i.e., ground state) to a reactive intermediate capable of forming covalent bonds with appropriate materials.
Such latent reactive groups can be used, for instance, to first derivatize a target molecule (e.g., thermochemically), in order to then photochemically attach the derivatized target molecule to a surface. Such a sequential approach is suitable in many situations, but can lack such attributes as speed, versatility, and ease of use, particularly when used with target molecules that are inherently difficult to first derivative, or need to be used under conditions that would result in loss of desirable (e.g., biological) activity.
In another approach, the surface itself can be provided (e.g., derivatized or “primed”) with latent reactive groups, which can then be activated while target molecules are in sufficient proximity to become thus attached to the surface. For instance, Applicant's U.S. Pat. No. 5,414,075, describes the use of linking agents to prime a surface to provide the surface with photoactivatable groups. This patent describes a restrained, multifunctional reagent useful for priming a support surface, or for simultaneous application with a target molecule to a support.
By contrast, there appear to be relatively few examples of surface coatings that are provided by the formation of polymers in situ upon the surface, e.g., by grafting. For instance, Tazuke et al. discuss the modification of polymer surfaces by the use of a grafting technique that involves treating a base polymer (e.g., polypropylene) with a reacting solution that contains sensitizers (e.g., benzophenone) and a selected polymer to be grafted onto the base polymer. “A Novel Modification of Polymer Surfaces by Photografting,” Tazuke et al., pp. 217-241, in Modification of Polymers, ACS Symposium Series 121 American Chemical Society, 1980. The use of polymeric photosensitizers for initiating polymerization has also been described. See, for instance, “Radical Polymerization,” C. H. Bamford, pp. 940-957 in Kroschwitz, ed., Concise Encyclopedia of Polymer Science and Engineering, 1990.
Moreover, Applicant's own U.S. Pat. No. 5,741,551 describes the manner in which molecules of reactive chemical unit can be bonded to a surface, via the activation of latent reactive groups. In turn, a different monomer, oligomer or polymer can be covalently bound to the reactive chemical unit, and in turn, to the support surface, for instance, by means of a polymerization reaction between the two.
In a related manner, Applicant's U.S. Pat. No. 5,714,360 describes a chemical linking agent comprising a di- or higher functional photoactivatable charged compound. The linking agent has increased hydrophilic character, as compared to the reagents of the '075 patent above. Applicant's co-pending International PCT application No. PCT/US99/21247 further provides a method for the use of reagents of the type described in the '360 patent as coating agents for forming a polymeric layer on a surface by graft polymerization. In its Background section, the co-pending PCT application describes common methods of attaching a polymer to a support surface, including the attachment of a preformed polymer to a surface, and grafting a polymer to a surface.
PCT Publication No. WO 99/15917 (Baron, Novartis AG) describes a method for treating the surfaces of siloxane-containing hydrogel contact lenses. The publication describes the manner in which preformed polymers are grafted onto a surface using photogroups (such as benzophenone) as photosensitizers. In a first treatment, the surface is functionalized by dipping it in a solvent solution containing the photosensitizer. Thereafter, the functionalized surface is contacted with a solution containing macromer, which is grafted to the surface upon the application of UV light.
PCT Publication No. WO 01/17575 (STS Biopolymers, Inc.) describes a method for graft polymerization of substrate surfaces. The publication describes a method of coating a substrate, involving exposing a substrate to an initiator capable of initiating a graft polymerization reaction on the substrate, to generate reactive radical sites on the surface of the substrate; contacting the substrate with a composition comprising one or more monomers in a medium which has different hydrophilicity compared to the substrate, and grafting monomer molecules onto the substrate by forming covalent bonds between monomer molecules and the substrate at reactive radical sites on the substrate surface.
See also Anders et al., U.S. Pat. No. 6,096,369, which describes a process for making the surface of polymeric substrates hydrophilic. The process includes coating the surface with a solution of a “macroinitiator,” after which a hydrophilic vinyl monomer solution is then applied and the system activated in order to provide the free radical polymerization of the monomers to the surface.
On a separate subject, a variety of approaches have been described for use in providing coatings upon porous substrates. For instance, Applicant's U.S. Pat. No. 5,744,515 describes the manner in which porous materials such as vascular grafts can be coated with adhesion molecules in order to promote capillary endothelialization once positioned in vivo. In one embodiment, the adhesion molecules themselves bear photoreactive groups, in order to permit the molecules to be contacted with the surface and immobilized upon activation of the photoreactive groups.
A relatively new type of medical device is referred to as a “distal protection device,” for use in filtering blood in situ, downstream from the site at which an interventional procedure is being performed. Examples of such devices are described, for instance, in U.S. Pat. No. 6,245,089. However, no teachings appear to exist in the art regarding either the ability or desirability of providing polymeric coatings on such devices, particularly in a manner that does not substantially alter their desired performance characteristics.
Indeed, Applicant has found that the above-described approaches and reagents, whether for attaching derivatized polymers, or for grafting polymers onto surfaces, tend to be of considerably less utility for surfaces having particularly small pores, interstitial spaces or apertures that are intended to remain open and unclogged in the course of their intended use. Such pores and the like can tend to be clogged, particularly by the use of relatively hydrophilic coating agents, which tend to “web” over the apertures, thereby jeopardizing the uniformity and/or utility of the thus-coated article.
To the best of Applicant's knowledge, the art does not teach, nor are there commercial products that involve, the preparation or use of nonpolymeric coating agents that are themselves attached to the porous surface of an article in order to initiate photopolymerization from the surface. Moreover, there remains a need for coating agents that can be used to coat relatively hydrophobic surfaces, and particularly for those surfaces that provide relatively small pores, interstitial spaces, or apertures.